Preparation And Absorbing Properties Of Nickle-foam-based Composite

In the current research of microwave-absorbing materials,absorbing materials with good conductance have excellent conductivity loss.However,high conductivity can lead to bad impedance matching,which limits the development of such materials in the field of microwave absorption and even they do not get enough attention.Thus,improving the impedance matching of absorbing materials with high conductance is of far-reaching research significance.Commercial nickel foam(NF)has excellent mechanical properties and interconnected three-dimensional conductive network structure but with poor impedance matching.Therefore,by coating it with dielectric materials such as porous carbon,Zn O and graphene sheet(GS),the dielectric loss mechanism will be introduced without damaging its unique structural advantages to improve impedance matching,while retaining excellent attenuation ability of nickel foam.In this thesis,the preparation process of C-Zn O@NF composite was optimized,and then the absorbing performance of C-Zn O@NF composite with different coating thicknesses was studied.And a simple exploration of the preparation process of GS@NF composite was carried out.By simulation,the effects of the structural sizes of NF and the coating thickness of GS@NF on absorption performance were studied.Through the characterization of morphology and structure,C-Zn O@NF with multi-interface heterogeneous structure was synthesized and the preparation process was optimized as follows: in the aqueous solution,the stirring time,the reaction temperature,the concentration of Zn(NO3)2 and the heat treatment temperature were 1min,25°C,0.0375 M and 500°C,respectively.The coating layer becomes thicker as the number of coating times increases.When the coating time is 1,the obtained C-Zn O@NF has the best microwave-absorption performance with the reflection loss value of-26.18 d B at 5.2GHz and the effective bandwidth of 1.78GHz(4.64GHz?6.42GHz)at the thickness of 2.5mm,due to the value of normalized impedance |(5|(closer to 1)and the increased attenuation ability.The precursor of GS@NF composite material can be prepared by a simple solution-impregnation method.Taking the tetrahedron as the minimum periodic unit of the NF,its absorbing performance can be adjusted by changing the size of its cell or rib.The relatively better performance of NF with small cell size or large rib diameter is at low frequency,while that of NF with large cell size or small rib diameter is mainly at higher frequency.As the GS-layer thickness increases,the reflection loss curves of GS@NF built based on the modle of NF shift to th left with smaller peak values and wider effective bandwidth.When the thickness of coating layer in GS@NF composite is 14?m,two obvious loss-absorbing peaks appear with the reflection loss-14.56 d B and-14.41 d B at 12.5GHz and 14 GHz,repectively.Besides,its effective bandwidth can even reach 5.1GHz.Moreover,by analyzing the energy density distribution and electric field of GS@NF(the thickness of coating layer is 14?m)at 13.8GHz,it is shown that the presence of GS allows more electromagnetic waves to enter the composite,enhances the impedance matching of NF,and makes GS@NF have stronger attenuation ability due to the introduced dielectric loss.